1. Field of Invention
The present invention relates to a power transmission system, particularly to a power transmission system for a four-wheel drive vehicle, which includes a countershaft type transmission device as a principal transmission mechanism, a sub transmission mechanism, and a power transfer system.
2. Description of Related Art
Where a continuously variable transmission as disclosed in Japanese Patent Application Laid-open No. 8 (1996)-21503 is used for a power transmission system of a four-wheel drive vehicle, there has been a demand that a sub transmission mechanism is employed to widen a transmission range of the power transmission system, in order to achieve both off-road and on-road abilities and improve fuel economy and silence.
Since a power transfer system is generally combined with the continuously variable transmission, the power transmission system becomes heavy and long in its axial direction. This causes changes, for example, in a propeller shaft and a casing (transmission case and power transfer system case), resulting in cost increase.
The object of the present invention is to provide a lightweight and compact power transmission system at low costs, with a sub transmission mechanism assembled to a basic structure of a countershaft type transmission device and a power transfer system.
An aspect of the present invention is a power transmission system comprising: a transmission device including an input shaft to which a drive force from a motor is inputted, a transmission mechanism arranged coaxially with the input shaft, and a countershaft parallel to the input shaft; and a power transfer system for distributing the drive force transmitted to the countershaft to front and rear wheels, wherein the power transfer system includes a sub transmission mechanism coaxially arranged in an end of the countershaft.